Extension Study To Evaluate Safety And Tolerability Of 24-Hour Daily Exposure Of Continuous Subcutaneous Infusion of ABBV-951 In Adult Participants With Parkinson's Disease

An AE is defined as any untoward medical occurrence in a participant or clinical investigation participant administered a pharmaceutical product and which does not necessarily have a causal relationship with the treatment. The investigator assesses the relationship of each event to the use of the study drug or device as either reasonable possibility or no reasonable possibility. A serious adverse event (SAE) is an event that results in death, is life-threatening, requires or prolongs hospitalization, results in a congenital anomaly, persistent or significant disability/incapacity or is an important medical event that, based on medical judgment, may jeopardize the participant and may require medical or surgical intervention to prevent any of the outcomes listed above. Adverse Events of Special Interest (AESI) - polyneuropathy, weight loss, hallucinations/psychosis, and somnolence will be monitored throughout the study.

The Infusion Site Evaluation Scale will be used to assess infusion sites. Infusion Site Evaluation Scale is an eight-point numeric scale used to assess irritation at the infusion site area (0 being "no evidence of irritation" and 7 being "strong reaction spreading beyond the test site").

The Infusion Site Evaluation Scale will be used to assess infusion sites. Infusion Site Evaluation Scale is an A to G letter grade scale, used to assess irritation at the infusion site area (A being "no finding" to G being "Small petechial erosions and/or scabs").

Number of participants with clinically significant change from baseline in laboratory parameters (hematology, biochemistry, coagulation, and urinalysis) will be reported throughout the study.

Number of participants with clinically significant change from baseline in vital signs will be reported throughout the study.

Change from baseline in 12-lead ECGs on heart rate, RR interval, PR interval, QRS duration, and QT interval will be monitored throughout the study.

Average normalized daily "Off" Time (Hours) is assessed based on Parkinson's Disease (PD) Diary.

Average normalized daily "On" time is assessed based on Parkinson's Disease (PD) Diary.

PD symptoms will be assessed by the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Parts I-IV.

The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.

Quality of life is assessed by the PD Questionnaire-39 items (PDQ-39). PDQ-39 is a disease-specific instrument designed to measure aspects of health that are relevant to participants with PD, and which may not be included in general health status questionnaires.

Each item is scored on a 5-point scale.

Health-related quality of life is assessed by the EuroQol 5-dimensions questionnaire (EQ-5D-5L).

EQ-5D-5L is a standardized instrument that consists of 2 parts: the EQ-5D descriptive system and the EQ visual analogue-scale (EQVAS).

Cognitive impairment is assessed by the Mini-Mental State Examination (MMSE). MMSE is used to assess orientation, attention, immediate and short term recall, language, and ability to follow simple verbal and written commands. The test consists of five sections (orientation, registration, attention-calculation, recall, and language) and results in a total possible score of 0 to 30, with higher scores indicating better function.